Supporting arm for sound boxes and sound recorders



Jan. 19, 1943. R. VERMEULEN 2,308,795

SUPPORTING ARM FOR SOUND BOXES AND SOUND REC-ORDERS I Filed June 24, 1939 Patented Jan. 19, 1943 SUPPORTING ARM FOR sounn BOXES AND UND BECOBDERS Roelof Vermeulen, Eindhoven, Netherlands, as-

signor,-by mesne ration of America, tlon of Delaware Application assignments, to Radio Corpo- New York, N. Y., acorpora-t June 24, 1939, Serial No. 280,949 Germany August 5, 1938 3 Claims. (01. 179-10041) With mechanical sound-recording and sound reproducing devices, it has been sought to make the supporting arm for the sound recorders and the sound boxes so as to be as simple as possible and nevertheless sufllciently stiff and free from resonance. The usual forms of construction are constituted by a hollow body of metal or synthetic resin, in the internal part of which extend the supply conductors for the speech coil.

According to this invention, the voluminous and heavy construction is abandoned, since the supporting arm itself is only constituted by a plurality of supply conductors which have together a sumcient stiffness and a very low ohmic resistance.

It is one of the marked advantages of this construction that the cross-section oi the supporting arm need not exceed the size necessitated by' mechanical requirements with a view to bringing about only an inappreciable loss of energy in theJO supply conductors even with sound boxes and sound recorders having a low internal resistance, say, of the order of magnitude oi 0.01 ohm. With the usual forms of construction, in which the supply conductors extend in the internal part of the supporting arm, it may be the case that the cross-section of all of the supply conductors necessitates a larger diameter of the supporting arm than would be necessary for reasons of mechanical strength.

Even if this condition were not imposed, the known supporting arms are always given such a size that their mechanical impedance maintains U-shaped cross-section, the conductor a few forms of construction shown in the accompanying drawing, wherein Fig, 1 represents one embodiment in which the supporting arm is constituted by'a still! and a flexible aperiodic supply conductor, v Fig. 2 shows one form of construction in which both supply conductors extend concentrically with respect to one another, Fig. 3 shows a supporting arm of four supply conductors parallel-connected in pairs, and

Fig. 4 shows a modified form of supporting arm for a pickup device of the type shown in Fig. 3. Referring to Fig. 1, I0 is the sound boxor pickup device whose scanning needle I I may scan the sound grooves of a sound record l2. The vibrations of the needle ll produce, in the armature coil l3, A. C. voltages which are conducted through supply conductors I4 and it to an amplifying device which is not shown in the drawing. The supporting am it is pivotally journalled in a joint ll of the supporting body IS.

The supporting arm I8 is constituted by a stiff supply conductor IQ of copper or aluminum having an U-shaped cross-section. Owing to this IS has a sufficient stiifness to act as a supporting arm for i the sound box. The second supply conductor is the movements of the arm due to the resonance vibrations below a definite limit judged to be admissible. However, if the arm according to the present invention is only constituted by a plurality of supply conductors, thecross-section of which is only determined by the maximum admissible electric resistance, then the mechanical impedance of the arm may frequently not suffice to avoid resonance vibrations.

In order to render these vibrations harmless, however, at least one of the supply conductors by which the arm is constituted is preferably so formed that it has the required stillness against bending and torsion, while the other ,supply conductors are in mechanical .contact with the former and increase the internal friction of the arm. They thus exert a damping action upon vibrations, ifany, of theformer supply conductor.

Further features and advantages of the inven-'- tionwill be more fully-explained by reference to laid as an insulated copper cord 20 in the. U-

shaped opening of the conductor l9. One endof the armature coil I8 is connected to the supply conductor it through the housing of the sound box i0 and the external supply conductor is fixed therein. The other end of the coil I3 is directly connected to the cord 20 which, in turn, is connected to the supply conductor I4.

In the form of construction according to Fig. 2, the external supply conductor 2| is constituted by an aluminum tube the internal diameter of which is completely filled up by an insulated copper conductor 22. One end of the tube 2| is stiiily secured to the housing 28. of the sound box or pickup deVice its other end carrying the ball joint 24 by means of which it bears in a movable manner on the supporting body 25. One end of the armature coil 26 is'directly connected to the adjacent end of the copper conductor 22, and the other end thereof is connected to the housing 23, the tubular conductor 2|, and the ball joint 24. A conductor 21 establishes the electrical connection of the ball 24 with thev amplifying device which follows. Y [I The aluminum tube It has a sufiicient stiffness to serve as a supporting arm. For damping the natural resonance of this tube, its internal diameter is completely filled up by the compound -'no resonance and has a may, of course. be

the supporting arm is formed by four supply conductors which are parallel-connected in pairs. One supply conductor is constituted by an aluminum tube in which the non-insulated cop per cord 30 is enclosed almost throughout its length. The second supply conductor is, according to the same construction, constituted by an aluminum tube 32 which is separated from the former and in which is enclosed the copper cord 88 which is likewise not insulated.- Only in the vicinity of bearing points II and It are'the cords SI and 83 not surrounded by the tubes 20 and 32 but form, themselves, the flexible suspension points. They are then led, insulated from each other, to the amplifying device through the supmagnetic field in a rod-like manner porting body The other ends of the supply conductor 29 and 32 are connected, respectively, to the covers it and 31 oi the housing 38 of a pickup device. The armature it of this pickup device is constituted by a'single supply conductor vibrating in a and stretched between the covers It and 31. One end of the the ball 42 and in the cover II of the sound box.

This tube forms one supply conductor and is in itself: suiiiciently stiff against bending and torsion to serve as a supporting arm. Inside this tube and concentrically thereto at some distance from the inner wall of the'nrst tube, there is a second tube 44 which is led in through the sound box to the second cover 11. and serves as a second supply conductor. 7

tubes. 43 and 44 is maintained in such manner that a helically wound yarn thread 45 is laid between "the tubes. This yarn thread causes a great friction between the external and the internal tube, thus damping vibrations, if any, of

'lating device adapted to cooperate with a phonesupport said device and constituting armature 39 is connected to outside through the cover 31 and carries a. hard pin 40 as a scanning needle. Such sound boxes have been described in detail and claimed in the U. S. patent application Ber. No. 214,608 of R, Vermeulen et al., now Patent No. 2,240,918, grantedMay 6, 1941. The resistance of the armature is in general rather. low. (1. e., approximately 0.01 ohm) so that it is necessary that the supplyand carrying-oi! conductors should have a lower resistance. At the same time, this sound box has, however, in itself, a very low weight (1. e., lower than grams, viz, approximately 16 grams), and also the pressure of the needle III in the sound groove must be less than 30 grams so that it is also necessary to maintain that part of the weight of the supporting arm, which presses upon the sound box, as low as possible. This condition is particularly important since such sound boxes have a noninterchangeable needle. In order to increase the life of the needle as'much as possible, the pressure of the sound box on the sound record is maintained very low (via, below 30 grams) and the directivei'orce of the armature also is low (via, less than 20 grams) at a normal amplitude of 0.1 mm.

Fig; 4 shows another embodiment of a supportingarm for the same sound box. The supporting body I carries a ball Joint 42 having a hollow ball into which lead two concentric tubes 48 and M which form together the supporting arm. The external tube 43 is electrically connected in a mechanically rigid manner both in 0 8 1 8. said member maintaining said the'external tube. It serves also as an insulating body between the supply conductors. The supplyand carrying-on conductors l8 and 4'! serve for-the connection to cord It i connected to the cord 41 to the ball ing the internal friction of the supporting arm,

the internal tube 44 and the intermediate space, may, if desired, still be filled up with wax.

I claim as my invention: I x v 1. In electrical signal translating apparatus, the combination of an electromechanical transgraph record and including a conductive casing and signal voltage generating means within said casing, a conductive member of substantially U- shaped cross section electrically connected to said casing. said member having suilicient stiflness to the sole supporting means therefor, said casing having electrical connection with said voltage generating means, a second conductive'member electrically connected to aid voltage generating means, said second-named member .being located between the sides of said U, and means for maintaining said conductive members equally spaced from each other throughout their common lengths.

a 2. In electrical signal translating apparatus, the combination of an electromechanical trans-, lating device adapted to cooperate with a phonograph record and including a conductive casing and signal voltage generating means within said casing, a conductive member of substantially U- shaped cross section electrically connected to said support said device and constituting the sole supporting means therefor, said casing having electrical connection with said voltage generating means, a second conductive member electrically connected to said voltage generating means. said second-named memberbeing located between the sides of said U, and means electrically insulating said members-from each other and conductive members equally spaced from each other throughout their common lengths.

3. The invention terized by the tween said conductive members,

set forth in claim 1 characsaid damping means being of a character which exhibits appreciable internal friction.

ROELOF The distance-between both the amplifying device. The

42. For further. in'creas-.

having sumcient stillness to addition of damping means he 

